An Investigation on Sparsity of CapsNets for Adversarial Robustness

The routing-by-agreement mechanism in capsule networks (CapsNets) is used to build visual hierarchical relationships with a characteristic of assigning parts to wholes. The connections between capsules of different layers become sparser with more iterations of routing. This paper proposes techniques in measuring, controlling, and visualizing the sparsity of CapsNets. One essential observation in this paper is that the sparser CapsNets are possibly more robust to the adversarial attacks. We believe this observation will provide insights into designing more robust models.